I have always wondered why the excise is higher on diesel in the UK. A higher price for diesel is shared in europe only by Switzerland and Liechtenstein. Was it once that only industry used diesel engined transport and the voting public used petrol and it was politically easier to tax industry?

In trying to reduce carbon dioxide emissions and hydrocarbon consumption it seems perverse to have a higher tax on the more efficient fuel.

Whatever the original reason it should be changed now. TOD readers would probably wish to see this done by raising the price of petrol but we are in a small minority and I suspect the best we can hope for politically is a tax neutral adjustment of both prices.

This differential is probably the reason Mercedes Benz decided not to produced a right hand drive two seat diesel Smart car at 88mpg which would be zero tax disk and only the petrol version at 66mpg and £25/year tax disk

The excise tax difference is not that great, but you are right, it should be lower.  However, it should not be so much lower that it encourages people to purchase a higher-powered diesel than they would otherwise.